Carbonyl sulfide is an important compound which is attracting attention as an etching gas for highly anisotropical and highly selective etching of an organic antireflective coating by plasma. Conventionally, a process of reacting carbon dioxide with carbon disulfide and a process of reacting sulfur with carbon monoxide have been known as a process for producing carbonyl sulfide.
For example, U.S. Pat. No. 4,120,944 (Patent Document 1), U.S. Pat. No. 3,409,399 (Patent Document 2), and Japanese Examined Patent Publication No. S47-40632 (Patent Document 3) describe a process of reacting carbon dioxide with carbon disulfide in a gas phase in the presence of a catalyst. Such process, however, suffers from reduced activity of the catalyst. Known examples of the process of reacting sulfur with carbon monoxide to produce carbonyl sulfide include a process of conducting the reaction in a gas phase and a process of conducting the reaction in a liquid phase. As examples of the process of conducting the reaction in a gas phase, Japanese Examined Patent Publication No. S56-45847 (Patent Document 4) and Japanese Examined Patent Publication No. S61-5409 (Patent Document 5), for example, describe a process of reacting sulfur with carbon monoxide in the presence or absence of a catalyst. In such process, the sulfur used in excess is required to be separated, and there is fear of the formed carbonyl sulfide decomposing because of high temperature. The process which uses no catalyst requires a very high reaction temperature and thus requires use of an expensive corrosion-resistant material.
Known examples of the process of reacting sulfur with carbon monoxide in a liquid phase to produce carbonyl sulfide are described in the following patent documents.
(1) U.S. Pat. No. 2,992,896 (Patent Document 6) describes a process for producing carbonyl sulfide, the process including suspending an aliphatic tertiary amine and hydrogen sulfide in an aliphatic alcohol solvent and reacting sulfur with carbon monoxide in the suspension.
(2) U.S. Pat. No. 2,992,897 (Patent Document 7) describes a process for producing carbonyl sulfide, the process including reacting sulfur with carbon monoxide in an aliphatic alcohol solvent having dispersed therein a sulfide or a bisulfide of an alkali metal or an alkaline earth metal as a catalyst.
(3) U.S. Pat. No. 2,992,898 (Patent Document 8) describes a process for producing carbonyl sulfide, the process including reacting sulfur with carbon monoxide in a medium of a hydroxy substituted tertiary aliphatic amine.
(4) U.S. Pat. No. 3,235,333 (Patent Document 9) describes a process for producing carbonyl sulfide, the process including reacting sulfur with carbon monoxide in the presence of an alkali metal carboxylate, an alkali metal formate, an alkali metal acetate, an alkoxide of a metal of Group I, II, and III, tetramethylguanidine, or potassium formate as a catalyst at a temperature of from 50° C. to 150° C. and a carbon monoxide pressure of from 200 psig (1.38 MPa) to 5000 psig (34.4 MPa).
(5) Japanese Unexamined Patent Publication No. 561-197414 (Patent Document 10) describes a process for continuously producing carbonyl sulfide, the process including reacting a secondary aliphatic amine with carbon monoxide and sulfur using selenium (Se) as a catalyst to form a thiocarbamic acid amine salt, thermally decomposing the formed thiocarbamic acid amine salt into carbonyl sulfide and a secondary amine, and reacting the secondary amine with carbon monoxide and sulfur.
(6) International Patent Application Publication No. WO2004/089824 (Patent Document 11) describes a process for producing carbonyl sulfide, the process including dissolving sulfur in carbon disulfide and reacting it with carbon monoxide.